Communication switching system



Nov. 26, 1940. w. v. K. LARGE 2,222,672

COMMUNICATION SWITCHING SYSTEM Filed March 2, 1958 4-Sheets-Sheet l a N .oz .Amin v W 'Y ign Nov. 26, 1940. w. v. K. LARGE 2,222,672

COMMUNICATION SWITCHING SYSTEM Filed March 2, 1938 4 Sheets-Sheet 2 UNA? REcAL o/sc Uhr.

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POLA RIZ D /NVENTOR #ulg/LARGE ATTORNEY Nov. 26, 1940. W, v K LARGE 2,222,672

COMMUNICATION SWITCHING SYSTEM Filed March 2, 1938 4 Sheets-SheelI 3 POLAR/ZED POLAR/Z50 A 7' TOR/VE V NOV. Z6, 1940. W- v K` LARGE 2,222,672

COMMUNICATION SWITCHING SYSTEM Filed March 2, 1938 4 Sheets-Sheet 4 Illlf-ilI @LM-f1 IDLE l INDYICTOR /NVENTOR @y wiz/LARGE A 7` TORNE V Patented Nov. 2,6, 1940 r UNITED STATES OFFHC.

COMMUNECATION SVVITCHING SYSTEM Wayne V. K. Large, Glenwood Landing, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 2, 1938, Serial No. 193,477 14 claims.. (ci. 17e-e) This invention relates to improvements in In the accompanying drawings, Fig. l is a manual communication switching systems and schematic diagram disclosing the new arrangeparticularly in telephone, telegraph and teletypement of this invention for handling combined writer manual switching systems. local and long distance traffic;-

More particularly it relates to improvements in Fig. 2 is a block diagram Showing tile intel- 6 switching arrangements in switchboards for hanrelation of Figs. 3, 4 and 5 herein; dling combined local and long distance trahie Fig. 3 is the cord circuit used for extending and to improvements in certain of the circuits subscribers line circuits either to a long distance used in performing these functions, namely, the trunk t0 a distant Oilee Ol fOr eXteIldiIlg silbcord circuit, the operators position circuit and the serbers lille Circuits through a COmDletiIlg 10 completing trunk circuit-, v trunk, per Fig. 5, to another switchboard inthe An object of this invention is Ato provide im- Salne OiiiCe, WhiCh handles all iHCOmiYlg Calls proved switching arrangements incommunication both local and long diStarlCe, Wlleie they ae fili'- switchboards for handling combined local and ther extended to a local subscribers line. AIn l5 long distance traflic Fig. 3 relay 3H 'performs the function of split- 15 A feature of this invention is that theswitchtins the Cord and terminating the repeater in boards are arranged so that local and long disthe cord associated with the answering end of tance traflic originate in one switchboard which the 00rd, and at the Same time terminating the extends the long distance traffic directly to a long trunk repeater t0 Which the Calling end of the distance trunk. The local traflic, instead of being cord is connected; v 20 completed in the originating board istrunked to a Fig. 4 is the ohelators position circuit. This second board, which completes all incoming trahie circuit is individual to each position and comtoth local and long distance. This feature is mon to each cord per Fis. 3 at each position. shown herein as applied to a manual teletype- The operator lockout relays, which prevent more 25, writer switching system, but itis applicable to all than one operator from being COmeCted t0 a 2li known manual switching communication systems. subscribers lille at any 011e time by' baiirlg all A further feature of this switchboard is a reoperators when more than one is connected to duction in the number of apparatus units required a subscribers line are relay Lliiii, Tela-Y 4i@ and per operators position, to provide what is known relay @l i; and as the operator lockout feature. This feature Fig. 5 is a- 01lrWire repeater Circuit Used fOl" 30 prevents more than one operator from answering interboard lconnection within the ofce. It an incoming call at any one time. The apparatus functions only on local calls to connect a subrequired per position has been materially reduced, scrbers line from the board in which all calls by the design of a position' circuit, which prooriginate, to the board in' which all calls are vides the feature for each cord to which it is concompleted. It includes a repeater, namely, re- 35 nected. The apparatus is furnished once per lays 5MB, 5d? and their associated connections. position instead of being included in each cord. Refer now to Fig. l which shows the vnew This modification, to make possible furnishing manner ofv handling incoming and outgoing the operator lockout device but once per positraliic according to this invention. Fig. 1 pro- 40 tion, instead of for every cord at a manual vides an arrangement for handling all outgoing switchboard, is shown herein as applied to a traine, both local and long distance in one switchteletypewriter switching system, but it is apboard, and all incoming traffic both local and plicable to all manual communication switching longk distance and all through long distance systems. traiiic in a second switchboard. Tov do this, the A further feature of this invention is that in answering jacks and line signals associated with the `cord circuit', which includes a telegraph rethe subscribers lines appear in one switchboard, peater, one relay only per cord is used to split the outgoing board only, and the calling jacks, and terminate the calling and answering ends by means of which calls are completed to subofthe cord. scribers in the local area served by the central A further feature of this invention is that it station, and which are a multiple of the answer- 50 provides a four-wire trunk including a repeater ing jacks, are segregated in a second switchboard for intra-office interboard'use. in the same olrlce. This second switchboard These and other features will become apparent handles all incoming traiTic to the local area,v from a consideration of the following description both local and long distance. It is used, also, and the appended claims. as a through board to extend toll calm.` The 55 outgoing long distance calls are extended directly from the originating switchboard over long distance trunks to a distant oice, where they may be completed to subscribers in the local area served by the distant oiiice, or further extended to a more distant oice. The outward switchboard in the first central ofce in this arrangement, handles outgoing long distance calls directly, without the use of an intervening toll board.

Although in telephone practice it is old to provide a separate outgoing and incoming switchboard, separate toll boards are provided for use in conjunction with these boards, when the traino is so divided, for handling toll traiiic and such tramo is not handled directly by the incoming and outgoing boards.

In Fig. 1, a calling subscriber is represented by the circle marked Sub. I. This may be any of the subscribers served by central station I. Sub. I line has connected to it an answering jack with which is associated a signal, usually a lamp, in switchboard I. The answering jack and lamp have multiple appearance before various operators in switchboard I. Subscriber I has, in addition, connected to his line in switchboard 2, multiple jacks, whereby a call for his line may be completed. All of the subscribers lines in the local area served by central station I are similarly arranged. Let us assume that Sub. I wishes to call Sub. 2. In response to his signal at switchboard I, the operator at one of the positions where Sub. I signal appears, will insert a cord into the associated jack. An operators position circuit is connected to this cord. The subscriber passes a number for Sub. 2, connected to the same central station. The operator will not complete the call in switchboard I, but will extend the call to switchboard 2, by means of the local completing trunk. The operator at switchboard 2 will connect a cord and her position circuit to the trunk. The necessary information for completing the call will be passed to the operator at switchboard 2, who will thereupon complete the call to one of the called subscribers multiple completing jacks.

If instead of calling a subscriber connected to central station I, the subscriber calls another subscriber, Sub. 3, in a distant area, the operator at switchboard I- will extend the call to a second central station in the distant area, directly over a long distance trunk, if it can be reached directly, or through a second central station to a more distant central station, by means of a number of long distance trunks and central stations in tandem. The latter condition is represented by the chain connection through central stations 2 and 3 in the upper portion of Fig. 1.

In the lower portion of Fig. l a diagram of connections for a call is shown, originated by Sub. i in a distant area. This call is extended through central stations 4 and 5 to switchboard 2 in central station I. Here the call may be completed to the multiple completing jack of any subscriber connected to central station I or it may be extended, if the call isA for a more distant subscriber, to a distant oiiice over another long distance trunk.

One of the advantages of this Inode of handling traine lies in the facility with which calls may be handled, by relieving the operator at switchboard 2 of the duties of an operator at an originating switchboard, such as timing the calls, etc. Another is the obvious advantage of eliminating the separate toll switchboards.

'Ihis tranic arrangement does not involve new subscribers line circuits. The subscribers loop and line circuit shown in Figs. 1 and 2 of C. C. Lane Patent 1,965,383, July 3, 1934, will function with this invention and this patent is hereby made part of the present application as if fully included herein. When Fig. 2 of Patent 1,965,383 is used multiple jack appearances are provided as indicated in Fig. 1 herein. The line circuits used may, in addition to that shown in Patent 1,965,383, be any of a number, well known in the art. Neither is it limited to line circuits in which either the answering jacks or calling jacks have multiple appearances in their respective boards. It may be used where there is a single answering ,jack connected to the line appearing in switchboard I, and a single calling jack connected to the line in switchboard 2, but, in the preferred embodiment, there are multiple answering jacks in switchboard I and multiple calling jacks in switchboard 2. Further, this traffic arrangement is not limited as to the other circuits involved, but may be operated with various cord and trunk circuits well known in the art. As applied in the preferred embodiment, use is made of well-known line circuits, long distance trunk circuits and the cord and position circuits at switchboard 2. In order to facilitate switching operations, however, various novel features have been introduced into the cord and operators position circuit at switchboard I and a novel completing trunk is provided to interconnect switchboards I and 2. The general relationship of these circuits is indicated by the diagram of Fig. l in which the cord circuit and position circuit of switchboard I are shown as well as the local completing trunk connecting the boards. It is further illustrated in the block diagram of Fig. 2 and in the following detailed description read with reference to Figs. 3, 4 and 5.

The subscribers line circuit, with which the cord circuit per Fig. 3 functions is provided with multiple line signals and answering jacks which are located at a number of positions in the originating switchboard, so that a calling subscribers line may be answered at a number of positions. The associated line signal at each position, usually a lamp, indicates that a particular line is calling. In response to this signal any of the operators, at the positions where the line signals appear, may answer the call by rst operating typing key 308 of any idle cord, all of which are identical with Fig. 3, at said position, and thereafter inserting the answering plug 3llI` of the same cord into the line jack associated with the signal. Key M5 in Fig. 4 is operated whenever the operators position is occupied.

The operation of the cord typing key 388 cuts the operators position circuit per Fig. 4, of which there is but one per position, into the circuit, to associate it with the cord whose typing key has been operated. The operation of key 398 also operates relays BIIS! and 305 in parallel, over a circuit from ground, through the upper armature and front contact of key 338, through the windings of relays 339 and 305 in parallel, to battery. The operation of relay 3BE extends the sleeve circuit of the connecting line circuit, not shown, through the sleeve of plug 30|, through the upper inner front and break contact of relay 303, the lower armature and front contact of relay 305, into Fig. 4, through the upper winding of polarized relay fill), relay III winding, to a mid-point of the potentiometer formed by battery through resistance 424, lower armature and front contact of key 4 I 5,

resistance 423 to ground. If the cord vcircuit which we are `considering 'is the rst cord circuit to answer the call, a .condition on the 'sleeve of the connecting Vline circuit will operate relay 4| 0 armature to its right-hand contact and will also operate relay 4| l. Relay il operated will furnish battery through its lower armature and front contact, through relay 4&5 winding, to ground, operating relay 4535. Relay 405 will furnish ground, through its single front Contact and armature, relay 4 i il armature and right-hand contact, through the lower winding of relay'llil into Fig. 3, through the upper middle front con-l tact and armature of relay 3dS, through the windings of relays 3133 and 353 in parallel, to battery, operating relays 3'3 and 353. After the operation of relayf405, relay 94 il] will lock momentarily over the holding path through Vits lower winding, heretofore traced, to insure a proper sequence of operation. The operation of relay 3|@ in Fig. 3 will close'a circuit from ground, through the left-hand inner armature and front contact of relay 3l3, through resistance; 335 and'328, through the lower winding of rela;7 3| through the armature and right-hand contact of relay SI2, resistance 33|, to positive battery. The operation of relay CH3 will also close a circuit, from. ground, through the right-"hand inner armature and front contact of relay 3|3, through resistances 329 and 321, lower winding of relay 3|2, through relay 3|! armature and right-hand contact, resistance 333 to positive battery. The operation of relay ac3 in Fig. 3 will extend the transmission conductor of the line circuit, through the position circuit of Fig. 4 back to the repeater in Fig. 3. This circuit may be traced, from the ring of plug so l, through the uovper middle front and back contacts of relay through the back and front contacts associated with the upper middle armature of relay 309, into Fig. 4, through the upper armature and break contact of key 432, key 492 being unoperated, through the right-hand upper and lower break contactsK of lkey 4M, key 46| being unoperated, the upper winding of relay 4|9, through break key 42|, the sending contacts 422. the leit-hand lower and upper break contacts of key 41M. back into Fig. 3, through the front and back contacts associated with the upper outer armature ci relay 309, through the upper winding of relay 3| I, the armature and right-hand contact of relay 312. resistance 33| to positive battery. The other side of the repeater is closed, from positive battery,

through resistance 333, right-hand contact armature of relay 3| l upper winding of relay 3i?. resistance 325, break contacts associated with the upper outer armature of relay .3|5, upper outer and inner armatures and back contacts of relay 3i? in parallel, break contacts of the make-before-break combination associated with the upper middle armature of relay Slg, right-hand outer make contact andl armature of relay SiS, resistance 33B to positive battery. The operation of relay 393 will also open the path from plug 3i!! sleeve, heretofore traced, the break contacts of the make-before-break combination associated with the upper inner armature of relay 363, through the lower armature and front contact of relay Sil, upper windingof relay 4| il and relay 4| i winding. The operation of relay soli, further, transfers the sleeve connection of plug 30|, through the upper inner front contactand armature of relay resistance 323, through the winding of relay Sd to battery, operating relay 354. The operation of relay 394 furnishes ground, through its single front contact and armature, to hold relays 3513 and 3f3operated, under control of the plug 351|. The operation of relay 3&3, also transfers the tip di plug `30|, from the busy test lead tothe busy test relays, M16-and 407 in the position circuit, Fig. 4, t'o the winding of relay 3636 in the cord circuit.

If an operator at lanother position has "inserted a cord into a multiple jack associated with the same line, so that the cord which we are considering is a second or subsequent cord to answer the call, the condition on the sleeve of the associated jack will be changed. in a manner well known in the art, due to the connection of the interfering cord or cords. Under these circumstances, relay i411 will not operate to its right-hand contact. Relay 4| I wil-l, however, operate in turn operating relay 485. When relay M5 operates, acircuit will loe closed from ground through relay M55 front contact and armature, relay M0 armature and left-hand contact, relay 499 winding lower front contact and armature of relay 4| l, resistance 425, to battery, operating relay 4F39. When'relay 439 operatesp'ositive battery is connected through relay 469 lower outer front contact and armature, through the upper inner front contact and armature of relay '3139, to the transmitting conductor of the cord at the ring of plug 353|. The circuit will be extended from the ring of plug sill of the second and subsequently connected cords. lif any, through the ring circuit of the multiple jacks, into the ring of plug 30| of the rst cord, over the communication circuit, through the cord and .position circuit of the rst cord, to rneet positive battery through resistance This deenergizes the line and releases relay 4|9. When the line is deenergized it is impossible to transmit by operating .key contacts 422 and receiving relay Mil is maintained permanently on its right-hand or spacing Contact. The operator at the rst position will be unable to communicate, because rher keyboard is locked, even though her communication-circuit .is'otherw-ise complete. As .the relays of the second and subsequent cordsdo not operate, the transmission circuits for these cords andthe associated position circuits are open, and the operators at these positions cannot communicate with theA subscriber.

When relay 469 operates in the second and subsequently connected cords, if any, a vcircuit is closed from ground, through the lower inner armature and front contact'of relay 481, through lamp 4|-3 and resistance 435 to battery. This is a signal for these cords to be disconnected. Disconnection removes positive battery on the ring or transmitting conductor of the first cord, unlocking the associated position keyboard and the calling subscriber and operator at said position may communicate. It is to be observed that the relays which perform the lockout function, namely, relays `M5, 439, 4|!) and 4H, are located in the position circuit, Fig. 4 and are therefore required only once per position since Fig. 4 is common to all cords at a particular position, being associated with a particular cord only lwhile the typing ykey 363 of that cord is operated. After the called number has been passed to the operator and the operator has eX- tended the call to the succeeding switchboard and the subscribers are in communication. the operator disconnects her position circuit from the rparticular cord and the position circuit is available for connection to another cord.

The operation of the receiving relay 'M9 and its associated apparatus will now be described in detail. It has been explained that key 4|5 in the position circuit per Fig. 4 is operated whenever the position is occupied. When key 4|5 is operated, negative battery is furnished through its upper armature and front contact, resistance 432, lower winding, which is the biasing winding, of polar relay 4|9 to ground. When current iiows through both windings of relay 4|9, the relay armature is operated to engage its left-hand contact. When the path through the upper winding of relay 4I9 is open or when it is connected to battery of the same polarity at each end, the relay armature will be operated to its right-hand or spacing contact under the iniiuence of its biasing winding. When the armature of relay 4|9 is on its left-hand 0r marking contact, relay 418 is operated over a path from negative battery, through the front contact and lower armature of key 4|5, resistance 4||y winding of relay 4I8 to positive battery, operating relay 4|8. When relay 4|9 is on its spacing contact, the path through relay winding 4|8 is shunted to positive battery through the spacing contact and armature of relay 4I9 to positive battery. Relay 4|8 is slow to release, and is held operated on ordinary spacing signals, releasing only when the relay 4|9 armature remains on its spacing contact for a relatively longer interval, as when a break signal is sent. With relay 4|8 operated and relay 4|9 on its left-hand or marking contact, a circuit may be traced from positive battery, through relay 4|9 armature and left-hand contact, armature and front contact of relay 4I8, printer magnet 420 winding, resistance 4|1, lower armature and front contact of key 4|5 to negative battery, operating printer magnet 420. When relay 4|9 armature is operated to its right-hand or spacing contact, the path through printer magnet 420 is open and the magnet releases. Magnet 420 will therefore follow the marking and spacing signals of relay 4|9. During a break signal, or when the lockout device operates to prevent the rst .operator from communicating and relay 4|9 remains on its righthand or spacing contact, relay 4| 8 releases. Positive battery is then connected through the make-before-break contacts of relay 4|8 to printer magnet 420 to hold the magnet energized and prevent spinning.

Under certain special circumstances, although the board at which cords per Fig. 3 and position circuits per Fig. 4 are located will be used to extend outgoing calls only, it may be necessary for an operator at said board to call a local subscriber connected to said board. To do this the operator will first operate key 308 of a cord, Fig. 3 and then test the subscribers line jack to see if the line is busy at some one of the positions in the same switchboard, on a call originated by the subscriber in which he is the calling party, or at some position in the associated switchboard, on a call in which he is the called party.

If the line is busy, due to one of such calls, there will be negative potential impressed 0n the sleeve of all multiple jacks, due to the cord already connected to the line. The operator will rst operate key 308 of a .particular cord, and touch the tip of plug 30| connected to said cord to the sleeve of the jack associated with the line she wishes to call. A circuit will thus be closed, from negative potential on said sleeve,

through the tip of plug 30|, the upper outer armature and back contact of relay 303, the relay being unoperated, the lower armature and front contact of key 308 into Fig. 4, through the upper armature and back contact of relay 4| I, relay 4| I also being unoperated, through relay 401 winding to ground. Relay 401 is a polar relay, operating on negative potential. It will therefore operate, closing a circuit from ground, through its armature, lamp 4|3, resistance 425 to battery, lighting lamp 4|3, indicating a busy line. 1

When a subscribers line is out of order it is a practice to so arrange the line that an operator making a busy test on said line may be informed of the out-of-order condition. This is performed by imposing on the sleeve circuit of said line a condition differing from the busy condition. An out-of-order cord, not shown, is plugged into any one of the jacks associated with the subscribers line which is out of order. Positive battery is connected to the sleeve of the plug of said cord. The sleeves of all of the jacks connected to the line both in the originating board and in the completing board are multiplied together. The positive battery condition on the sleeve is therefore available wherever a jack appears. When an operator tests the line under these circumstances by touching the tip of plug 30| to the sleeve of the jack, relay 406 operates. Relay 406 is a polar relay in parallel with relay 401 and operates on positive potential. The operation of relay 406 in turn operates relay 408 and lights lamp 4|3 over an obvious circuit. The operation of relay 408 in turn operates buzzer M2.` The operation of the buzzer and the lighting of the lamp together indicates an out-of-order as distinguished from a busy condition.

If the line is neither busy nor out of order, the operator will insert plug 3| into the line jack. Ground on the tip of the jack will operate relay 306. Relays 303, 304, 305 and 309 will operate as heretofore described. A circuit will be closed from negative battery through resistance 339, left-hand outer armature and make contact of relay 3|3, upper armature and make contact of relay 306, lower armature and front contact of relay 309 into Fig. 4 t0 the lower armature of key 402 to terminate the repeater over a circuit heretofore traced. The operator will then operate key 402 in Fig. 4. The operation of key 402 will close a circuit from ground through a source of ringing voltage 4|4, through the upper front contact and armature of key 402 into Fig. 3, through the make-before-break contact combination associated with the upper middle armatures of relays 309 and 303 in series, to the ring of plug 30|, where it is extended through the ring of the subscribers line jack to the subscribers line, to operate the subscribers station ringer in any of a number of well-known manners. The operation of key 402 will also remove the negative battery furnished from relay 3|3 to terminate the repeater and apply terminating negative battery directly through the make-before-break contact combination of key 402 over the transmission conductor through the position and cord circuit, heretofore traced to positive battery on the righthand contact of relay 3|2 to hold the calling end of the line closed. This transfer is made during ringing to guard against the opening of the repeater when the subscriber answers and the ground on the tip of the line jack is removed which would release relay 306 and remove the negative battery opening the repeater and sending a, false signal toward the. calling side of the cord.

In extendingV a call, the cord circuit per Fig. 3 may be connected either to a long. distance trunk to a. distant. office, or toa local trunk to a switchboard inthe same oce for completion to a local subscriber. The connection to the longA distance, or toll trunk as itis otherwise known, is themore frequent and the manner in which Fig.. 3 functions on sucha. connection will be described first. 'Ihe long distance trunk itself, with which the cord functions, isnot new, and, as it operates in its usual well-known manner, it is not shown,` as it is not necessary to an understanding of the invention herein.

When the operator has received. the number of the desired subscriber, and a toll connection is required, she will. insert the. calling cord plug into the toll line jack, if idle, as indicated by the idle indicators, associated with thetoll line trunk jack. Ground is connected to the sleeve of the trunk jack. A circuit will be closed from this ground through the sleeves of the jack and plug 32l, resistance 324, winding of relay 320 to battery, operating relay 32B. Relay 32B operated, closes an obvious circuit to operate relay 3 9. 'I'he operation of relay 3|.9 will disconnect the transmission lead from negative battery, through resistance 338, and connect it, through the front contact and middle armature of relay 3| 9, the ring of plug 32|, over. the transmitting conductor of the toll trunk, -to the distant oiiice. The operation of relay r319 also transfers the tip of r; the cord, from the lead to the busy test and outof-order relays, to a path, through the: righthand armature and lower contact of key 3M, relay 3|? winding, to battery. Relay 3|? does not operate at this time, however, as the tip connection is open in the trunk circuit. The operator now calls over the toll trunk, by operating the left-hand armatures of non-locking key 3M. A circuit will thereupon be closed, from ground, through the front contact and bottom armature of key 3M, through relay 3|5 winding, to battery,

operating relay 3|5. The operation of relay 35 will open the line towards the toll line and close negative battery through resistance 338, upper outer armature and front contact of relay 3|5,

resistance 325, upper winding of relay 3|2, armature and right-hand contact of lrelay 3| I, resistance 333 to positive battery, to hold the repeater and the subscribers line in the marking condition. 'I'he operation of key 3M will alsofurnish battery,

zthrough its front contact and top armature, to

the winding of relay SI5, but relay 3|6 will not operate as the connection to ground is open at relay 3l?, which is unoperated. The open to the toll line brings up a lamp at the distantl oice, in any of a number of well-known manners. When key 3M is restored to normal, relay 3l5 will release. When the distant operator answers, the circuit is ready for transmission.

If the call is to be completed over a trunk to "l the switchboard in the same oirlce which completes calls `to local subscribers, since Fig. 5 has multiple jack appearances at each end, plug 32| is inserted into jack 53| of the rst idle trunk. If a trunk is busy, lamp 552 is lighted, from ground, through a source of potential 534, through lamp 532 to ground. The chain circuit which controls the idle indicating feature, indicated by 525, is well understood in the art, and functions in its well-known manner. Upon plugging in,A a circuit is closed, from batterythrough relay 323 winding in Fig.. 3, resistance 324, sleeve of plug 32| into Fig. 5, sleeve of jack 58|, through relay 5.05 winding: to ground, operating relay 535. Relay 555, on operating, furnishes ground, through itsv bottom armature and front contact, for the parallel circuits, through relay 5|5 lefthandi winding to battery and through relay 5|? winding, the left-hand break contacts of the make-before-break contact combination on relay 5|6 to battery, operating relays 5|5 and 5|?.r Relay 535 alsov extends the ring circuit of the cord, whichis the; communication conductor, through its. upper inner armature and front Contact, resistance, 5H, upper winding of relay 505, relay 55? armature and right-hand contact, through resistance 52| to negative` battery.

Relay 535 also connects the tip ofthe trunk to ground, at the upper outer armature and back Contact of relay 538. This provides the ground 'necessary for the operation of relay 3|? in the cord over a circuit heretofore traced. The operation of relay 3|? lights lamp 322, over a circuit,

from ground, through the lower outer front contact and armature of relay 3| through the lament of 'lamp 322, into the position circuit per Fig. 4 through the winding of relay 453 to battery.

Relay 5.65, when operated, connects ground, through the inner armature of relay 5|5, to the lower or balancing windings of relays 536 and 50?, through resistances 51|'2 and 5M respectively. The operationof relay 5l5; also connects positive battery, through resistance 526, right-hand outer armature and frontcontact of relay SI5; the break contacts of the make-before-break contact combination of relay 5,38, resistance 513 upper winding of relay 55?, armature and make contact of relay 53B, resistance 523, tol negative battery, to hold relay B operated. Relay 5l?, operated, applies ground to the night alarm, over a circuit, from the left-hand inner armature and front contact. of relay 5|?, through relay 558 winding, to battery, operating relay 5&8. The operation of relay 5|8 operates the alarm 5|9 over an obvious circuit. Relay 5l? connects battery, through its left-hand outer armature, in parallel, tothe idle indicating circuitwhich functionsin a well-known manner and through the .righthand, armature and back contact of relay 5|6, through lamp. 5|0 filament, to ground. The answering lampv 5|Bv is lighted as a signal toV the operator at the completing board, otherwise known asinward board, to answer the call.

The cord circuit per Fig. 3 of Lane Patentv 1,965,383, mentioned above, will serve as the cord circuit at the inward board. This circuit is well known in the art and functions in a well-known manner. It will be usedv at the inward boardV to interconnect the incoming end of the local `completing trunk per Fig. 5 and the multiple jack of the subscribers line circuit. This operation will not be described indetail here. But the manner in which the vcompleting trunk functions when this connection is made will now be described.

rI'he inward operator answers by'inserting plug of her cord circuit into jack 539. There, is battery on; the connected sleeve of the inward cord; A circuit is extended from this battery, through the sleeve of jack 559, through relay 553 winding, to ground, operating relay 538. erated, transfers the ring, which is the transmission circuit, from positive battery on the back contact of the make-before-break contact combination of relay 558, to the upper inner armature-of relay 508 and extends the circuit, through Relay 538, op- 'I' the ring of jack 500, into the cord and through a line winding of a repeater relay to positive battery on the marking contact of a repeater relay in the cord.

Relay 500, operated, also applies ground through its lower front contact and armature to the right-hand winding of relay 515 and to the winding of relay 518 in parallel, operating relay 518. Relay 515 which is already operated is now under control of both sleeve relays 505 and 508. Relay 503 also disconnects ground from the tip of outward jack 501 and the multiple connection of that jack, to the tip of inward jack 509 and its multiple connections. Relay 518, operated, extinguishes answering lamp 510 and locks up, through its left-hand innermost armature and front contact under control of the bottom front contact and armature of relay 505 and hence relays 505 and 508 must both be released before relay 515 will release. Relay 516 also opens the circuit, heretofore traced, through the winding of relay 511 which is slow to release. Before relay 511 releases, it connects battery, momentarily, from the left-hand outer armature and front contact of relay 515, through relay 511 righthand armature and front contact, to the sleeve of jack 501, shunting the battery on the sleeve of the cord Fig. 3, through relay 320 winding and resistance 324, to release relay 320. Relay 320 released, momentarily releases relay 319, which breaks the holding path of the calling cord, flashing lamp relay 313, from battery through the lower winding of relay 310, through the lower outer back contact and armature of relay 316, the top inner front contact and armature of relay 310, through the top inner back contact and armature of relay 305 to ground, by opening the circuit at the top inner front contact and armature of relay 319. This prevents lamp 322 from flashing, if the operator has withdrawn from the connection, for, as will be hereinafter explained, in a description of the cord lamp flashing recall feature, the flashing recall is obtained by momentarily operating relay 311, by providing a momentary ground. This operates and locks the ashing recall relay 318 for the calling cord. Upon the removal of the momentary ground the calling lamp 322 is transferred from the steady ground, on the lower outer front contact and armature of relay 311, to the flashing lamp circuit, from interrupter 31, through the top armature and front contact of relay 318, the lower outer back contact and armature of relay 311, through the lamp filament, to battery through relay 403 winding in Fig. 4. All of the other functions performed by relay 511 are now performed by relay 516 when relay 511 releases.

Relays 506 and 501, with their associated resistances and battery connections, form a telegraph repeater, which permits the connecting together of two cord repeaters both of which are equipped for positive battery marking. Reference to Fig. 3 and the above description discloses, that when the answering plug 301 is connected to the line jack, and relay 313 is operated, battery flows through both windings of the repeater relays and the repeater assumes the position shown, which is the marking position. With the armature of relays 311 and 312 on their righthand contacts, positive battery is connected to the line windings of each relay. For the marking condition, therefore, the cooperating repeater connection in the trunk is terminated in negative battery for the marking condition. The

cord in the inward board is arranged with positive battery on the marking contacts of its repeater relays. Therefore the repeater connection in the trunk cooperating with the cord has negative battery on its marking contact. Signals received from the outward board will operate relay 505 which will apply negative and positive battery to the inward board but will not operate relay 501 because of its diierential characteristic. Likewise, signals from the inward side will operate relay 501 but will not operate relay 505.

Reference to Fig. 5 discloses that when relays '505 and 505 are operated, the tip connection between the boards is continuous. This path is therefore available for supervisory signaling between operators. When the operator at the inward or completing board recalls theoutward board, ground is applied momentarily to the tip or jack 509 and then the tip circuit is opened. When the ground is applied a circuit is closed from ground, through the tip of jack 509, the top front contacts and armatures of relays 500 and 505, through the tip of jack 501, into Fig. 3, through the tip of plug 32 I, the top armature and front contact of relay 319, the right-hand armature and break contact of key 314, through relay 311 winding to battery, operating relay 311. Relay 311, operated, operates relay 318 over an obvious circuit and terminates the repeater in the cord in negative battery, through resistance 330 and the distant repeater in positive battery, through resistance 325. Relay 318 operated, locks, through its lower winding over a circuit heretofore traced. When relay 318 releases, a circuit may be traced, from ground, through the interrupter 31, the top armature and front contact of relay 318, the bottom armature and back contact of relay 311, the filament of lamp 322, into Fig. 4, through the winding of relay 403 to battery, flashing the lamp. To stop the ashing, the operator ,operates her typing key, actuating relay 305 and removing the ground from the holding path of relay 318 at the upper inner armature of relay 305. Relay 318 releases, opening the flashing lamp circuit.

When the inward operator in disconnecting removes the plug of her cord from jack 508, relay 508 will release, applying ground to the tip conductor of the trunk, at the upper outer armature and back contact. This will operate and hold relay 311 in the cord, Fig. 3, and light lamp 322 over circuits heretofore traced. The release of relay 508 will also connect positive battery to the line winding of relay 501. The operator at the outward board disconnects plug 321 from jack 501, releasing relays 505, 515 and 518 and restoring the circuit per Fig. 5 to the idle condition. The disconnection may `be started in the reverse order, plug 321 being first disconnected, releasing relay 505. This, similarly, places ground on the tip conductor, at the top outer armature and back contact of relay 505, which lights a lamp in the cord at the inward board. The release of relay 505 also connects positive battery to the line winding of relay 506, to hold its armature on its right-hand contact. When the outward cord lamp lights, the plug is dircennected from jack 509. Relays 508, 515 and 510 release, restoring the circuit per Fig. 5 to the idle condition.

The subscriber may recall the operator at the outward board. For this condition ground is connected momentarily to the tip conductor of plug 305, operating relay 306. The operation of relay 305 operates relay 301, from ground on the bottom front contact of relay 306, through the bottom armature, upper winding of relay 301, to battery. Relay till locks, from battery, through the lower winding of relay ltill, the bottom armature and front contact of relay 363, back contact and top armature of relay 305, lto ground. This closes a circuit, which remains closed after relay 3M releases, from ground, through interruptor Sihthe top armature and front contact of relay 301, the lower inner armature and back contact of relay 3dS, the filament of lamp 32 into Fig. 4, through` the winding of relay 493 to battery, flashing lamp 3132. The ashing may be stopped by operatingkey 368, which in turn operates relay 305, opening the holding path of relay 3d? and breaking the circuit of the flashing lamp.

For the subscriber disconnect condition, a permanent, instead of a momentary, ground is connected tothe tip of jack Sul, operating relay S, which remains operated and closes a circuit, from ground on the lower inner front contact of relay` 336, through the lower inner armature, lamp 3ii2v larnent, into Fig. 4l, through the Winding of;l relayl 433, to battery, lighting lamp 302 and operating relay 4&3, which in turn operates the alarm over an obvious circuit.

The functioning of the cord circuit per Fig. 3 on recall and disconnect signals received from a toll trunk is the same as described for the local completing trunk.

unas been shown that for flashing on either end of*` the cord, thek locking path through the hashing relays is completed tov ground through a contact on relay 3,05. This path is available only when relay 3&5 is released. The relay is under control of typing key 3&18, being operated whenever` the key is operated. Therefore, when the typing keyr is operated, neither lamp 352 nor 322- can be flashed. Flashing under these circumstances is unnecessary, because the operators position circuit is connected intothe circuit by the operation of typing key 368 and is available for. communica-tion. 'Ihe position circuit is equipped with a splitting key 46|, which is arranged to split the cord and connect the operators teletypewriter equipment to either the calling or. answering end of the cord, while terminating the opposite end in battery of the proper polarity. When the cord is so split the'end of the cord to which the position circuit is not connected be flashed. This is performed in the following manner.

For splitting the cord and connecting the positionteletypewriter equipment to one side or the other, typing key 3&3 is iirst operated, operating relays 3&5 and 399. To communicate with the subscriber, the left-hand armatures of key 4M are actuated. This connects negative battery through resistance 43|, the left-:hand upper armature of key QDI, intorFig. 3, through the upper outer make-before-break contacts of relay BBQ, upper winding of relay 3| l, armature and righthand contact of relay 3|32, resistance 33 l, to posi:- tive battery, holding relay 3H on its right-hand or. marking contact. The operation of the key also connects positive battery, through resistance dit), the left-hand lower armature and front contact of key 49|, typing keys 422, break key 42|, upper winding of relay M8, right-hand lower and upper break contacts of key fll in parallel, upper break contact and armature of key 462 into Fig. 3, through themake-before-break contacts associated with the upper middle armature of relay 399, the make-before-break contacts associated with the uppermiddle armature of relay 363, through the ring of plug 39| and thence over the, transmitting conductor of the subscribers line. IfV the right-hand armatures of key 40| are actuated, positive battery is connected to the answering side of the cord and` subscribers line, and negativebattery is connected through the positionV teletypewriter circuit in series` with the repeater on the calling side of the lineY over paths that should be obvious 'from the circuits last traced. When the cord is split and the position teletylewriter equipment is connected through the answering end ofthe cord to the subscribers line, the circuit is arranged so that itl is possible to flash lamp 322 associated with the calling end of the cord. This is accomplishedv by transferring the ground for the holding path o the calling cord dashing relay 3|8, from the upper inner armature of relay 305 which is not ayailable as it is operated as a result of the operation of thel typing key, through the make-beforebreak contacts associated with the upper inner armature yof relay 305, to ground onv the lefthand top make contact and armature of key 43| in Fig. 4. Similarly, when the cord is split and the position teletypewriter` circuit is associated with the calling end of the cord, it is possible for the subscriber to flash lamp 3,02 to attract the operator. This is accomplished by transferring ground for the holding path of the answering cord flashing relay 30,1 from the topl armatureof relay Miti through the make-before-break contact associated with this armature, to ground through the right-hand top front Contact and armature of keyl 4M. f

What is claimed is:

1. In atelegraph switching system, a switchboard, a telegraph line circuit connected to said switchboard, a first yoperators position anda second operators position in said switchboard, a jack connected to said line at each of said positions, a iirst cord circuit and a first operators circuit at said first position, a second cord circuit and a second operators circuit at said second position, means in said jack, cord and operators circuits at said-first and at said second position Afor forming with said line a continuous operable telegraph path, including said line, said irst jack, said first cord and said rst operators circuits or said line, saidsecond jack, said second cord and-said second operators circuits, and automatic relay means in said position circuits preventing the establishing of either operable path when both cords are connected to both jacks simultaneously.

2. In a telegraph switching system, a switchboard, a rst and a second position at said switchboard, a telegraph circuit connected to said switchboard, a rst answering jack at said first and a second answering jack at said second positions connected to said circuit in multiple, a, telegraph communication vlink circuit including one operators position circuit at each of said positions, means in said links. for connecting said link to said jacks at either of said positions to f form of said line, link and position circuits, a continuous operable telegraph path, and automatic relay means in said position circuits cooperating to make both paths inoperable when both of said links are connected to said jacks simultaneously.

3. In a telegraph system, a switchboard, an operators position at said switchboard, a telegraph circuit connected to a jack in said position, a plurality of cord circuits, and an operators position circuit at said position, a. telegraph communication pathineach 0I Said cord circuits, a

telegraph communication path in said position circuit, means in said cord and position circuits for connecting said position circuit individually to any one of said cord circuits, independent automatic relay means in said position circuit cooperating with relay control means connected to said jack for interconnecting or preventing the interconnection of said telegraph circuit, one of said cord circuits and said position circuit to form an operable telegraph path when one of said cords is inserted in said jack.

4. In a telegraph switching system, a switchboard, a plurality of operators positions at said switchboard, a plurality of communication link circuits at a plurality oi said positions, a continuous communication channel through each of said links, a position circuit at each of said positions, a communication channel in each of said position circuits, means in said circuits for dividing any of said link channels and means for connecting said position channel in said division to form with said link channel a continuous operable telegraph path at each position, a telegraph circuit connected to said switchboard, a plurality of jacks connected to said telegraph circuit, one of said jacks at each of said positions, automatic relay means also in said position circuits barring the interconnection of any of said continuous operable paths when more than one of said links is connected to said jacks simultaneously.

5. In a telegraph switching system, a switchboard, an operators position in said switchboard, a plurality of cord circuits and a single operators circuit individually connectable to said cords at said position and an operators lockout device in said position circuit.

6. In a communication switching system, a line circuit, a plurality of jacks in multiple connected to said line circuit, a plurality of cords connectable individually tosaid plurality of jacks, a plurality of operators circuits connectable individually to said cords, said line circuit cooperating with any of said cords and its associated operators circuit to form an operable communication path, and automatic relay means in said operators circuits preventing communication over any of said paths while more than one cord is connected to said jacks.

7. In a communication switching system a plurality of cord circuits, a plurality of operatois circuits connected to said cord circuits individually, and automatic relay lockout means in said operators circuits to prevent interference between operators when said cords are interconnected.

8. In a teletypewriter switching system, a first central station, a 'second central station, a third central station, a irst and second switchboard in said rst central station, a plurality of subscribers stations associated with said first central station, a plurality of subscribers line circuits connecting said subscribers stations and said iirst central station, a plurality of answering jacks and line signals connected to said line circuits in said rst switchboard, a plurality of calling jacks connected to said line circuits in said second switchboard, a plurality of long distance trunk circuits connecting said iirst switchboard and said second central station, a plurality of long distance trunks connecting said third central station and said second switchboard, a plurality of local trunks connecting said rst and said second switchboards, universal cord circuits at said first switchboard for extending long distance calls from said answering jacks to said long distance trunks, and for extending local calls from said answering jacks to said local trunks to said second switchboard and a plurality of universal cord circuits at said second switchboard for completing calls from said local trunks through said calling jacks to said subscribers stations and for completing calls from said long distance trunks from said third central station through said calling jacks to said subscribers stations.

9. In a manual teletypewriter switching system comprising a plurality of local subscribers stations in a first local area connected individually over telegraph circuits to calling signals and to answering jacks at a first switchboard and to completing jacks at a second switchboard, both of said switchboards at a first central station, manual cord circuits at said switchboards, local trunks connecting said switchboards, a plurality of other subscribers stations connected to switchboards in other areas remote from said first area and long distance trunk circuits connecting said switchboards directly or in tandem, the method of operation which comprises: (l) switching manually all calls originating in said first switchboard intended for subscribers in the local area served by said rst central station to said second switchboard; (2) switching manually al1 local calls incoming to said second switchboard to the called partys completing jack; (3) switching manually all calls originating in said rst switchboard intended for subscribers in remote areas directly from said first switchboard to switchboards in said remote areas over long distance trunks and (4) switching manually all calls originating in remote areas and incoming over long distance trunks to said second switchboard and intended for subscribers served by said irst central station directly from said trunks to the called partys completing jack.

10. In a manual teletypewriter switching system comprising an originating and a completing switchboard in one local area and a plurality of switchboards in remote areas connected to said originating and completing switchboards directly by long distance trunks, the method of handling local and long distance calls which comprises: (l) switching all local calls from an originating to a completing switchboard; (2) switching all long distance calls from said originating switchboard directly to a completing or through switchboard in a distant area; (3) completing all calls intended for subscribers in a local area whether originated locally or in a distant area in a separate completing switchboard.

11. In a manual teletypewriter switching system comprising a central station equipped with a first and a second switchboard, the method of traffic operation whereby alloutgoing calls only both local and long distance are interconnected from line circuits through cord circuits to trunk circuits at said rst switchboard and all incoming calls only both local and long distance are interconnected'from trunk circuits through cord circuits to subscribers line circuits for completing calls and trunk circuits for through long distance calls at said second switchboard.

12. In a teletypewriter switching system, a rst telegraph station, a second telegraph station, a four-wire telegraph trunk circuit connecting said stations and a single line repeater in said circuit.

13. In a teletypewriter switching system, a rst switchboard, a second switchboard, a four-wire telegraph trunk circuit connecting said switchboards, a single line telegraph repeater in said trunk and a supervisory wire in said four wires,

a sleeve and a signal conductor connecting said jacks and said lamps at said rst and said second switchboards with said relay equipment and a single line telegraph repeater in said relay equipment.

` WAYNE V. K. LARGE. 

